The invention relates to a method for monitoring slide bearings, especially of a piston engine, with a forced feed lubrication comprising a forced-oil line and branch lines branching off from the forced-oil line for the supply with oil of at least one slide bearing, with an operating parameter which changes on the occurrence of bearing damage being repeatedly measured and evaluated.
For the purpose of monitoring the slide bearings of piston engines it has already been proposed (EP 0161644 A2, DD 249075 A1, DE 19614803 A, JP 61105306 A) to monitor the temperature in the zone of the bearing box during the bearing operation in order to recognize any bearing damage announced by an increase in the temperature at an early time and to enable precautions to be taken for respective countermeasures. For this purpose temperature sensors are inserted into bores of the bearing supporting body, which bores extend in part up to the bearing box. The disadvantage in these known apparatuses for monitoring the temperature in the running layer zone is on the one hand that the bearing shells need to be tapped in order to avoid having to cope with longer response times for temperature detection which are caused by heat conduction and on the other hand that despite tapping the bearing shell at several places the response behavior is too sluggish when the damage which announces itself by an increase in the temperature is situated outside of the direct measurement zones which are determined by the position of the bores for the temperature sensors. Similar disadvantages occur when the lubricant pressure in the bearing clearance is detected by way of a bore which penetrates the bearing shell (JP 11072398 A) or when additional temperature sensors are provided in the zone of the measuring location for the lubricant pressure (EP 0029736 A1, JP 5782742A).
Since cracks occur in the bearing surface area towards the end of the service life of the bearing due to beginning material fatigue of the bearing surface material which lead to a local deformation of the bearing surface and subsequently to an increased metallic contact between bearing and shaft, it has also been proposed to use the thus caused change of the electric contact resistance between shaft and bearing for monitoring a slide bearing. The complexity of the measuring equipment required for this purpose is prohibitive, however.
The invention is thus based on the object of monitoring slide bearings, especially of piston engines, with a comparably low amount of effort without having to implement any measures on the slide bearings per se for detecting an operating parameter which changes upon the occurrence of a damage to the bearing.
Based on a method for monitoring slide bearings of the kind mentioned above, the invention achieves the object in such a way that the rates of oil flow and/or the oil pressures in the branch lines are measured and temporal changes to said operating parameters are evaluated for monitoring the bearing.
The invention is based on the finding that the local deformation in the bearing surface which is caused by the commencing fatigue of the bearing layer material and leads to an increase in wear and tear entails a progressively increasing bearing clearance in cooperation with a simultaneously occurring temperature increase at a respective dynamic bearing load. Said increase in the bearing clearance has an influence at a predetermined lubricant pressure on the rate of oil flow or at a given rate of oil flow on the oil pressure, so that by detecting the rate of oil flow and/or the oil pressure in a branch line the slide bearing supplied with lubricating oil through said branch line or the group of slide bearings connected to said branch line can be monitored concerning a commencing fatigue of the bearing layer material in a simple and effective manner. Since the oil demand of a bearing increases progressively in relationship to the bearing play, the beginning fatigue of the bearing surface material of a connected slide bearing can be recognized at an early stage through the measurement of the rate of oil flow and/or the oil pressures in the branch lines. The occurring changes concerning the rates of oil flow or the oil pressures need to be put in relation to the respective supply conditions of the lubricating oil in order to avoid erroneous evaluations concerning fluctuations in the supply pressure or supply quantities.
To ensure that changes in the rates of oil flow or the oil pressures in the branch lines can be brought into relationship in a simple manner with imminent damage to the slide bearings which are supplied with lubricating oil through said branch lines, changes in the rates of oil flow and/or the oil pressures in the individual branch lines can be compared with each other. Since one can assume that damage to bearings will occur individually and not simultaneously, it is thus possible, by a comparison of the changes of the rates of oil flow and/or the oil pressure arising in the zone of a branch line, to simply consider changes concerning the lubricating oil supply concerning the entire lubricating system with the respective measured values for the other branch lines, so that only increases in the rate of oil flow and/or the pressure loss in a branch line which deviate from said total changes are used for monitoring the bearing.